System for reception and transport of lime mud from a white liquor filter

Abstract

The system is for the reception and transport of dry lime mud from a continuously operating pressurized filter in a causticization process. A tube valve is used as an outlet from the pressurized process. The tube valve has a minimum length that is twice a diameter of the tube. A column of lime mud can be held within it as a pressure lock. The column of lime mud can be caused to descend through the tube valve by controlling a difference in pressure between an inner surface and an outer surface of the tube such that the diameter of the tube expands essentially uniformly along its length by 5-10% or by at least 4-6 millimeters.

Description

PRIOR APPLICATION[0001]This application is a U.S. national phase application based on International Application No. PCT / SE2008 / 051406, filed 4 Dec. 2008.TECHNICAL AREA[0002]The invention concerns a system for the reception and transport of dry lime mud from a filter medium in a continuously operating pressurised filter in a causticisation process, where white liquor is separated from the lime mud and where the lime mud in a dry state is transported to a lime kiln in a closed system.BACKGROUND AND SUMMARY OF THE INVENTION[0003]The green liquor that is a process liquor in the causticisation process consists principally of sodium carbonate. The green liquor is caused to react during the process with quicklime, whereby calcium carbonate (lime mud) is formed, together with sodium hydroxide (white liquor). The white liquor is filtered in tube filters or disc filters, where these filters, in particular the latter, are normally of pressurised type. The white liquor obtained is reused in the...

AI Technical Summary

Benefits of technology

The invention is a system designed to help output finely ground material from a pressurized process. Its purpose is to provide a more efficient and effective way to handle this material.

Problems solved by technology

This entails a number of unnecessary operations and a certain amount of unnecessary equipment in the form of sludging arrangements, storage tanks and dewaterers.

The conventional technology will be unnecessarily expensive since several additional stages, such as intermediate storage of the slurried lime mud in silos with continuous stirring and the subsequent dewaterers, are required.

Handling dry lime mud involves very serious problems since the lime mud produces dust and gives rise to environmental problems in the recovery process, and it is also highly wearing for processing equipment since the dry lime mud behaves as a grinding powder.

The wear means that handling equipment for dry lime mud from pressurised filtering processes cannot be constructed to use pressurised sluices having mechanical sealing arrangements with small tolerances since these parts wear rapidly.

Furthermore, dry lime mud is difficult to handle since the mud has a tendency to clog storage silos and pipe systems.

The systems, furthermore, must be able to feed the lime mud to the lime kiln in an even flow, since the kiln can easily damage the ceramic lining by burning, if the kiln is not evenly filled throughout its extent.

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